The city center (Moskovskaya Underground station) can be reached by the Bus or by Taxi. The transfer time is about 35 min. The detailed information about the transfer from/to airport is summarized here.
The Allegro train is a fast way to travel from Helsinki (Finland) to St. Petersburg. The train departs 4 times a day with a transfer time of approx 3.5 hours. Passport and customs controls are organized aboard the moving train and the authorities start inspections already after the train's departure. The train departs from Helsinki rail hub (in a city center) and bypasses a Tikkurila station, which is close to Helsinki airport (15 min by taxi).
Helsinki airport connection options are listed here.
Allegro arrives to St Petersburg-Finlyandsky rail hub, which is located in the city center, Underground station Ploshchad Lenina.
St. Petersburg Underground system is a fast way to navigate within a city. The Underground scheme can be found here.
The ICOE-2017 venue is located at Tekhnologichesky Institut station at the intersection of Red and Blue lines of the Underground in a city center.